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Abstract:

A RF electrode for generating, plasma in a plasma chamber comprising an
optical feedthrough. A plasma chamber comprising an RF electrode and a
counter-electrode with a substrate support for holding a substrate,
wherein a high-frequency alternating field for generating the plasma can
be formed between the RF electrode and the counter-electrode. The chamber
comprising an RF electrode with an optical feedthrough. A method, for in
situ analysis or in situ processing of a layer or plasma in a plasma
chamber, wherein the layer is disposed on counter-electrode and an RF
electrode is: disposed on the side lacing the layer. Selection of an RF
electrode having an optical feedthrough, and at least one step in which
electromagnetic radiation is supplied through the optical feedthrough for
purposes of analysis or processing of the layer or the plasma, and by at
least one other step in which the scattered or emitted or reflected
radiation is supplied to an analysis unit.

Claims:

1. An RF electrode for generating plasma in a plasma chamber, comprising
at least one optical feedthrough wherein the RF electrode is a
showerhead, and wherein a conical funnel lines the optical feedthrough of
the showerhead in a gas-tight manner.

2. The electrode according to claim 1, wherein the optical feedthrough is
large enough to allow in situ Raman spectroscopy or optical emission
spectroscopy to be carried out through the RF electrode.

3. An electrode according to claim 1, wherein the optical feedthrough has
a conical section.

4. The electrode according to claim 3, wherein the smaller of the two
openings of the feedthrough has an area of 0.03 cm2 to 5 cm.sup.2.

5. An electrode according to claim 3, wherein the larger of the two
openings of the feedthrough has an area of 0.031 to 100 cm.sup.2.

6. An electrode according to claim 1, wherein an opening of the optical
feedthrough comprises a shielding.

7. The electrode according to claim 6, comprising a metallic mesh as a
shielding tor the optical feedthrough, the mesh being disposed on the
opening of the optical feedthrough.

8. An electrode according to claim 1, comprising a converging lens.

9. The electrode according to claim 8, comprising a small glass plate for
protecting the converging lens against a gas in the plasma chamber is
disposed between the converging lens and the opening of the optical
feedthrough.

10. A plasma chamber, comprising an RF electrode according to claim 1 and
a counter-electrode with a substrate support for holding a substrate,
wherein a high-frequency alternating field for generating the plasma can
be formed between the RF electrode and the counter-electrode.

11. The plasma chamber according to claim 10, wherein a convex converging
lens disposed in the plasma chamber can focus electromagnetic radiation
through the optical feedthrough onto the layer or onto the plasma, and
radiation scattered or reflected through the optical feedthrough, or
radiation emitted from the layer or the plasma, can be parallelized and
supplied to an analysis unit for the purposes of analyzing the scattered
or reflected or emitted radiation.

12. The plasma chamber according to claim 11, comprising a converging
lens that can be moved in the beam path of the plasma chamber.

13. A method for in situ analysis or in situ processing of a layer or
plasma in a plasma chamber according to claim 10, wherein the layer is
disposed on a counter-electrode and an RF electrode is disposed on the
side facing the layer, comprising selecting an RF electrode and for
generating plasma in a plasma chamber having at least one optical
feedthrough at least one step in which the electromagnetic radiation is
supplied from the plasma chamber through the optical feedthrough in the
RF electrode to an analysis unit.

14. The method according to claim 13, wherein in situ Raman spectroscopy
of the growing layer or optical emission spectroscopy of the plasma is
performed, wherein the electromagnetic radiation is supplied to the
analysis unit, by way of a converging lens.

15. (canceled)

16. The electrode, plasma chamber or method according to claim 9, wherein
more than one gas distribution plate is disposed in the showerhead.

17. (canceled)

Description:

[0001] The invention relates to an electrode for generating plasma, a
plasma chamber comprising the electrode and a method for the in situ
analysis or in situ processing of a layer, or of the plasma.

[0002] The in situ characterization of an amorphous layer during plasma
enhanced chemical vapor deposition (PECVD) is known from Li et al. (Li,
Y. M., Ilsin A. M., Ngyuen H. V., Wronski C R., Collins R. W. (1991).
Real-Time-Spectroscopic Ellipsometry Determination of the Evolution of
Amorphous-Semiconductor Optical Functions, Bandgap, and Micrsotructure.
Journal of Non-Crystalline Solids. Vol. 137, 787-790). The authors used a
method of spectroscopic ellipsometry under irradiation with light at a
70° angle. Disadvantageously, the method and the ellipsometer used
only provide a comparatively limited amount of information on the layer
properties.

[0003] Wagner et al. (Wagner V., Drews, D., Esser, D. R., Zahn, T.,
Geurts, J., and W. Richter. Raman monitoring of semiconductor growth. J.
Appl. Phys. 75, 7330) describe in situ Raman spectroscopy of a layer
deposited using molecular beam epitaxy. The method and the design of the
device used are disadvantageous in that usage is limited in terms of the
type of deposition process.

[0004] The use of optical emission spectroscopy in situ for the plasma of
a plasma chamber is known from Dingemans et al. (Dingemans, G.; van den
Donker, M. N.; Hrunski, D.; Gordijn, A.; Kessels, W. M. M.; van de
Sanden, M. C. M. (2007). In-situ Film Transmittance Using the Plasma as
Light Source: A Case Study of Thin Silicon Film Deposition in the
Microcrystalline Growth Regime. Proceedings of the 22nd EUPVSEC (European
Photovoltaic Solar Energy Conference), Milan/Italy, Mar. 9, 2007-Jul. 9,
2007.-S. 1855-1858). Here, an optical feedthrough is provided at the
counter-electrode of the plasma chamber, the feedthrough being used to
examine the plasma directly through the substrate. This device is
unsuitable for collecting advanced information, which is also a
disadvantage.

[0005] The object of the invention is to provide an electrode for
generating plasma in a plasma chamber, the electrode being universally
applicable independent of the deposition process used, such as PECVD,
MOVPE, and independent of the testing method selected, such as Raman
spectroscopy and optical emission spectroscopy.

[0006] Another object of the invention is to provide a plasma chamber for
performing, in situ, a multitude of testing methods independent of the
layer manufacturing process.

[0007] Another object of the invention is to provide a method for
analyzing a layer to be deposited, as well as the process gases, in situ
while the manufacturing process is ongoing.

[0008] This object is achieved by an RF electrode according to the main
claim, a plasma chamber comprising such an electrode, and a method
according to the secondary claims. Advantageous embodiments can be found
in the respective dependent claims.

[0009] According to the invention, an RF electrode for generating the
plasma uses a high-frequency voltage. The plasma can be used for
depositing semiconductor layers or for plasma etching of semiconductor
layers, for example. In the first case, gases such as SiH4 or
H2 are introduced to the chamber, and in the second case, a gas such
NF3 is introduced.

[0010] According to the invention, the RF electrode is characterized by
comprising an optical feedthrough. The optical feedthrough advantageously
allows optical access to the plasma space itself and through the plasma
space to the substrate which is disposed at the counter-electrode (also
called the ground electrode). The passage of a beam path through the
optical feedthrough in the RF electrode according to the invention is
thus allowed. The advantageous effect is that it is possible to both
analyze and process the substrate and the layer growing thereon while the
plasma burns. A particularly advantageous effect of providing the optical
feedthrough in the RF electrode is that the plasma itself can also be
examined in the plasma chamber with regard to gas composition, and this
composition can be adjusted.

[0011] This provides a large degree of freedom in selecting the testing
method and the processing method.

[0012] In the context of the invention, it was found that the prior art is
limited with regard to the placement of an optical feedthrough in the
counter-electrode of Dingemans et al and with regard to the testing
method used in Li et al., as well as the deposition method in Wagner et
al. Only the RF electrode according to the invention allows a wide
variety of testing or processing steps for the layer and the plasma with
substantially every deposition method (PECVD, MOVPE and others) in situ.
By relying on the RF electrode according to the invention for both the
entrance to the plasma chamber and the issue of electromagnetic
radiation, the method according to the invention uses an angle of
incidence of approximately zero degrees relative to the layer to be
deposited. The advantageous effect of this is that even Raman
spectroscopy can be carried out on a growing layer, or locally resolved
optical emission spectroscopy can be carried out on the plasma, while the
plasma is burning (in situ). The processing of the layer can involve a
processing step with a laser.

[0013] It is especially advantageous that direct observation of a layer is
made possible by the optical feedthrough in the RF electrode by coupling
the light in and out at an angle of incidence of approximately zero
degrees relative to the layer. Minimal deviations from an angle of
incidence of zero degrees are conceivable.

[0014] In the prior art, on the other hand, the beam path for analyzing
the layer is irradiated at an angle of 70° relative to the layer.
This has the disadvantage that a large portion of the deposition space in
the plasma chamber is included, and thus incorrectly analyzed and
interpreted. In the invention, it was found that this form of in-situ
analysis generated incorrect results in the interpretation of layer
properties or plasma properties.

[0015] It was also found that, previously, primarily with small electrode
distances relative to the electrode surface, only an edge area of the
layer could be analyzed, or the production-relevant part could only be
analyzed at a specific angle. In the prior art, many investigations such
as Raman spectroscopy can only be carried out after the deposition has
been performed, as in Dingemans et al. The edge area of the layer refers
to that part of the growing layer that lies outside the optimum area of
electrode utilization, and thus that part which is irrelevant in terms of
subsequent use of the layer. This excludes certain measurement methods,
such as Raman spectroscopy or reflection spectroscopy, from being
particularly effective ways of characterizing a deposited layer in real
time, which is to say, during the deposition process. The term in situ in
the present patent application refers to the analysis or processing of
the substrate or a layer disposed thereon, or to be deposited thereon,
while the plasma burns, which is to say, in real time.

[0016] In contrast to the prior art. with the RF electrode according to
the invention, production-relevant areas of the layer can also be
analyzed and processed in real time, and not just the edge areas.

[0017] One particular such analysis is in situ Raman spectroscopy. By
coupling in a pulsed laser beam, via the optical feedthrough in the RF
electrode, onto the layer, and by way of spectroscopy of the scattered
light in direct back-reflection, Raman spectroscopy can be carried out
during the deposition, for example during deposition of material for a
thin-film solar cell. This makes it possible to better monitor the growth
and structural properties of the layer during deposition.

[0018] Another possible analysis method is spatially resolved emission
spectroscopy. Using a confocal design, with a fixed or moving lens in the
beam path, plasma emissions above a growing silicon surface can be
spectroscopically analyzed in a spatially resolved manner, which is to
say, at difference distances from the surface of the layer. The lens can
be fixed at the RF electrode. However, the lens can also be fixed inside
the housing of the plasma chamber. The lens can also be disposed movably
inside the housing so that a confocal measurement site is achieved for
different applications. Other methods, such as reflection spectroscopy
are also applicable. In addition, to achieve the same effect, the RF
electrode with the lens fixed thereto can be disposed in the beam path of
the measurement site so as to be mobile relative to the layer to be
examined.

[0019] The optical feedthrough runs through the RF electrode from the
surface on one side to the side of the RF electrode opposite thereto.
Thus, the feedthrough in the spirit of the invention involves an opening
through the electrode structure, the opening allowing the passage of
electromagnetic radiation, and in particular laser radiation, for
scanning in the direction of the growing layer. Meanwhile, the optical
feedthrough allows radiation issuing from the layer, or from the plasma
(i.e. reflection, scattering or thermal radiation) to be passed back to
an analysis unit. This also allows for measuring the temperature of the
layer. Accordingly, the electrode with the optical feedthrough is
disposed in the beam path of the radiation in-coupled into the plasma
chamber.

[0020] It is particularly advantageous for the electrode to be integrated
into a plasma chamber in which a vacuum can be generated. The electrode
is electrically insulated from the chamber wall. The RF electrode is
provided with a connection means for a high frequency alternating voltage
(RF connection: 30 kHz-300 GHz oscillation, preferably 13.56 MHz to
108.48 MHz). The alternating voltage of an RF generator is applied to the
metal plate serving as the electrode, which is located in a low pressure
chamber. Disposed parallel to the RF electrode and opposite thereto is
the counter-electrode with the substrate support.

[0021] It is advantageous for the vacuum chamber to contain a window in
the wall thereof as an optical feedthrough, through which the
electromagnetic radiation can be coupled in and out again.

[0022] The radiation out-coupled from the plasma chamber is advantageously
supplied through the lens and, if necessary, a mirror system, and is
focused onto the entrance slit of a spectrograph, such as an Oriel
Instrument MS260. The spectrograph is used to separate the radiation into
its spectroscopic components, which are analyzed by way of a CCD camera,
such as an Andor iDus 420. In the case of Raman spectroscopy, an optical
notch filter is disposed in the optical path from the substrate surface
to the spectroscope. The notch filter advantageously causes the
wavelength used to excite the Raman scattering to be limited to a very
narrow bandwidth.

[0023] In the simplest case, optical access to the layer, or to the plasma
above the layer, is by way of a hole, preferably in the center or near
the center of the RF electrode, so that production-relevant parts of the
substrate, or of the layer to be deposited, can be analyzed or processed.
This is not possible using electrodes according to the prior art.

[0024] It is particularly advantageous that the RF electrode comprises an
optical feedthrough that faces the plasma chamber, and that is shielded.
Shielding is preferably accomplished using a metallic mesh that is
disposed on the opening of the optical feedthrough. The advantage is that
of preventing disruption of the electrical field generated by the
electrode.

[0025] In the context of the invention, it was found that, depending on
the parameters of the deposition method being used, the optical
feedthrough can result in inhomogeneities in the layer deposition
process, or during etching, due to disruption of the electrical field.
Accordingly, the optical feedthrough, in the RF electrode, to the plasma
space, is shielded, preferably by way of a metal mesh, so that optical
access is possible with minimal loss. The advantageous effect is that the
high-frequency field generated by the electrode plates is largely
unaffected by the optical feedthrough.

[0026] This also applies in particular to the very advantageous case in
which the optical feedthrough is included in a showerhead electrode,
which serves as the RF electrode.

[0027] In this case, the optical feedthrough is integrated into the
showerhead electrode, which serves as the RF electrode, such that the
homogeneity of the gas distribution is not disrupted. This is achieved by
selecting a location for the optical feedthrough at which the gas passage
is affected by the optical feedthrough only at a few holes, or most
preferably at no holes. p The optical feedthrough and the metallic mesh
serving as shielding can be made of the same material, such as stainless
steel or aluminum.

[0028] The mesh shield can preferably be cut using a laser beam. The
thickness of the mesh webs can be approximately 0.3 mm and the width of
the webs can be approximately 0.1 mm, for example. Preferably, up to 12
to 19% of the opening of the optical feedthrough can be covered by the
webs of the shielding. Covering up to approximately 10% of the opening
with the shielding should be sufficient to maintain the homogeneity of
the plasma. While optimal shielding could also be achieved using a metal
plate, substrate or plasma analysis therethrough, or processing steps
therethrough, would of course be impossible. It is basically possible to
provide shielding with less than 10% of the area of the opening of the
optical feedthrough being covered. The precise percentage of covering of
the opening of the feedthrough by the shielding depends on the process
conditions, such as the pressure used in the plasma chamber. In the
deposition of microcrystalline silicon at a pressure of >18 Torr, an
electrode separation of 9 mm, a power density of ˜1 W/cm2 and
a growth rate of 0.5 nm/s, for a hole diameter of 1 cm facing the
substrate, no shielding of the optical feedthrough is required at all.

[0029] In the deposition of microcrystalline silicon at a pressure of 10
Torr, an electrode separation of 9 mm, a power density of 0.6 W/cm2
and a growth rate of 0.5 nm/s, for a hole diameter of 1 cm facing the
substrate, approximately 10% of the opening of the optical feedthrough
must be covered by the shielding.

[0030] In the plasma chamber according to the invention, if shielding is
provided, the opening of the optical feedthrough facing the deposition
zone is shielded. The entire vacuum chamber is generally referred to as
the plasma chamber.

[0031] In general, the optical feedthrough must be large enough to allow
the intended investigative process to be carried out through the
electrode according to the invention. This method can be in situ Raman
spectroscopy or optical emission spectroscopy, for example; or it can be
the determination of gas concentration through optical means. The area of
the optical feedthrough should be at least approximately 0.03 cm2.
For circular optical feedthroughs, this corresponds to a diameter of more
than 2 mm for the opening facing the deposition zone. Preferably, the
opening has an area of 1 to 10 cm2.

[0032] A lens can be disposed at the RF electrode, or in the plasma
chamber in general. The lens should focus the electromagnetic radiation
through the optical feedthrough onto the plasma, or the layer, or the
substrate. The same lens or, depending on the angle of incidence of the
radiation, a lens of another optical feedthrough in the RF electrode
parallelizes the electromagnetic radiation reflected or scattered or
emitted from the substrate, or the plasma, through the optical
feedthrough.

[0033] It is preferable for the angle of incidence of the electromagnetic
radiation onto the substrate or the layer to be zero degrees. Minimal
deviation from this angle is possible such that the angle of incidence
for access to the production-relevant part of the layer or discharge zone
is less than for access through the space laterally between the
electrodes.

[0034] Thus, the size of the optical feedthrough should in no way be
confused with the size of the openings of the holes in a showerhead
electrode according to the prior art, and consequently cannot be compared
with the same. These holes typically have a diameter of only
approximately 0.8 mm, which corresponds to approximately 0.005 cm2
of area. These prior art openings are unsuitable for analysis or
processing of the layer or plasma through optical means according to the
invention.

[0035] The optical feedthrough passes completely through the electrode.
Thus, the electrode comprises a first opening in the surface on one side
and a second opening on the surface of the electrode that is opposite
this opening. Both openings of the optical feedthrough can have the same
diameter. In this case, the electrode according to the invention can be
particularly easy to manufacture.

[0036] It is preferable for the optical feedthrough to have a conical
cross section. The optical feedthrough is then disposed in the electrode
conically. With a conical feedthrough, the opening facing the plasma
space has a larger area than the opening of the optical feedthrough that
is opposite that opening. This then advantageously allows electromagnetic
radiation issuing from the layer or the plasma to be collected and
supplied to the analysis unit more efficiently.

[0037] It was found that in the simplest case, the optical feedthrough can
be implemented by way of a single hole, for example a cylindrical hole,
in the electrode. For example, the RF electrode can be drilled using a 10
mm drill bit. However, it is also possible to instead make a conical
feedthrough in the RF electrode using a countersink bit.

[0038] The smaller of the two openings of a conical optical feedthrough
can have an area of 0.03 cm2 to 5 cm2. The larger of the two
openings of a conical optical feedthrough can have an area of 0.031 to
100 cm2. It is particularly advantageous for the area of the larger
opening of the optical feedthrough to be 20 times larger.

[0039] In general, the size of the opening facing away from the substrate
depends on the thickness of the electrode according to the invention at a
given cone angle.

[0040] Preferably, no gas flows through the optical feedthrough to the
plasma space, or exactly the same amount of gas flows as would flow from
the same area of an unmodified showerhead electrode. The advantageous
effect of this is that the homogeneity of the gas flow is not disrupted
by the optical feedthrough.

[0041] In addition to a simple hole in the electrode, an optical
feedthrough can also be designed as a component. This component lines the
hole in the electrode like a sleeve. In a showerhead arrangement serving
as the RF electrode, for example, three gas distribution plates of
different diameters are disposed one on top of the other, for example as
shown in FIG. 2. These plates form the showerhead serving as the RF
electrode. Holes of different sizes are provided in each of the three gas
distribution plates, so as to form the optical feedthrough. In the
electrode, these plates are arranged one on top of the other so that a
conical optical feedthrough is formed. In addition, a funnel-like conical
component for forming the conical optical feedthrough is disposed in the
showerhead. This component lines the optical feedthrough from the inside.
To accomplish this, the funnel comprises stepped support surfaces for the
gas distribution plates. Fixing means, such as screws, fasten the
plate(s) to the funnel. Advantageously, the wall of the funnel-like
component prevents the gas from flowing through the optical feed into the
plasma space. Here, the funnel acts as a gas seal for the optical
feedthrough.

[0042] Also, depending on the deposition process parameters, a metal mesh
can also be disposed on the smaller opening of the funnel-like component
as a shielding.

[0043] In another embodiment of the invention, a convex converging lens,
and in particular a plano-convex converging lens, is fixed at the optical
feedthrough in the RF electrode. This advantageously results in the
guiding of electromagnetic beam path through the optical feedthrough onto
the substrate, or onto the growing layer, or into the plasma, the beam
being focused onto the surface thereof for purposes of analysis or
processing. This makes it possible to generate a Raman emission from the
substrate or the layer by way of high energy input from a pulsed laser,
and thus to carry out Raman spectroscopy on the reflected radiation.
Also, the light, or in general the electromagnetic radiation, can be
gathered by the lens and focused, and also parallelized.

[0044] In this case the lens is disposed on the side of the optical
feedthrough not facing the plasma space. If additional shielding is
provided, the lens is disposed on the side of the opening that is
opposite the shielding.

[0045] It is particularly preferred that a replaceable small glass plate
for protecting the converging lens is disposed between the converging
lens and the opening of the optical feedthrough. This advantageously
prevents the lens from being coated while the plasma burns. The
advantageous effect is that the lens does not need to be removed when the
chamber is cleaned. Thus advantageously, the optics do not have to be
readjusted after cleaning.

[0046] A plasma chamber according to the invention comprises the RF
electrode with one or more optical feedthroughs and a high-frequency RF
connection.

[0047] Disposed in the chamber is a grounded or floating counter-electrode
with a substrate disposed thereon. A high-frequency alternating field for
generating the plasma is formed between the electrode and the
counter-electrode. According to the invention, the chamber comprises the
RF electrode with the optical feedthrough. This results in the
advantageous effect that electromagnetic radiation can be supplied
through the optical feedthrough onto the substrate or the layer growing
thereon, or into the plasma itself. In this way, the substrate, the layer
or the gas composition in the chamber can be tested in situ during
deposition and while the plasma is burning.

[0048] It is advantageous for the opening of the optical feedthrough
facing the interior of the plasma chamber to be shielded so that a
particularly homogeneous deposition or etching of the layer disposed on
the substrate is produced.

[0049] A convex converging lens on the side of the optical feedthrough
that faces away from the plasma chamber focuses the beam path onto the
substrate, or onto the layer growing on the substrate, or onto the plasma
itself. The lens gathers, focuses and parallelizes the reflected or
scattered radiation, or the radiation issuing from the sample surface of
the layer for the purposes of analysis. This means that the radiation
reflected or scattered or emitted from the layer is in turn gathered by
the optical feedthrough on its return path and is lead out of the plasma
chamber.

[0050] Thus, a uniform idea is that the RF electrode and the chamber
according to the invention enable a method for in situ analysis or in
situ processing of a layer in the plasma chamber and the plasma while it
is burning. The substrate is disposed on the counter-electrode.

[0051] The RF electrode is disposed on the side facing the substrate and
at a distance X from the substrate. The process gases used for the
deposition or etching are fed in and the process pressure is adjusted.
Then, the plasma is started.

[0052] In one embodiment of the invention, an electrode comprising an
optical feedthrough having a shielding on the side of the electrode
facing the substrate is selected for the method. It is particularly
advantageous that a plano-convex convergent lens is disposed on the side
of the electrode located opposite the shielding.

[0053] It is preferable to select a convergent lens that has a focal
length X plus the thickness of the electrode. The advantage is that a
beam path passing through the optical feedthrough is focused onto the
substrate. In contrast, reflected or scattered radiation, or radiation
emitted from the layer surface, is gathered and led from the chamber in
parallelized form by the lens. For this purpose and depending on the
design of the analyzing equipment and available space, the reflected or
scattered radiation, or the radiation emitted from the layer surface, can
first be supplied to a mirror.

[0054] It is particularly preferable for the plasma chamber to allow the
converging lens to move along the beam path. To this end, the lens is
movably attached inside the housing of the plasma chamber. A plasma
chamber is selected that has a support, which is attached to the
electrode in a height-adjustable manner. The lens can also be attached to
the RF electrode with the electrode itself being movable. Both
constructions provide the advantage that different areas between the RF
electrode and the layer, as well as the layer and the plasma itself, can
be variably spectroscopically investigated. The height-adjustability can
be ensured by way of a screw in a slot.

[0055] This allows the system to be adjusted to different lens and
electrode distances during the process. Furthermore, this facilitates
investigation of the growing layer and of the plasma. Of course, the
converging lens can be attached to the electrode itself for the method.

[0056] Preferably, in situ Raman spectroscopy is carried out. by way of
the collection of phonons by the converging lens, wherein the lens
focuses the light directed at the substrate onto the layer to be
investigated and the radiation reflected or scattered from the layer, or
the radiation emitted from the layer surface is led out of the chamber in
parallelized form.

[0057] According to the invention, the term layer is also meant to include
the substrate itself.

[0058] Below, the invention is described in more detail with the aid of
exemplary embodiments and the figures, but no limitation of the invention
is intended here.

[0059] Shown are:

[0060] FIG. 1: A section through the RF electrode and plasma chamber
according to the invention (schematic drawing).

[0061] FIG. 2: A section through the showerhead electrode according to the
invention (technical drawing).

[0062] FIG. 3: A section through the plasma chamber according to the
invention (schematic drawing).

[0063]FIG. 4: A section through the plasma chamber according to the
invention (technical drawing).

[0064] FIG. 5: The intensity of the Stokes shift is measured in situ as a
function of the magnitude of the shift, which forms the basis of Raman
spectroscopy, by way of the RF electrode construction according to the
invention with the optical feedthrough and placement in the plasma
chamber.

[0065] FIG. 6: The wavelength is measured in situ as a function of the
intensity as a basis for the determination of the SiH4 concentration in
the plasma chamber, by way of the electrode construction according to the
invention with the optical feedthrough and placement in the plasma
chamber

[0066] FIG. 1 shows the principle of the solution to the problem of the
invention using an optical feedthrough. The substrate 6 is disposed at
electrode 1, the counter-electrode. The RF electrode 2 according to the
invention comprises the optical feedthrough, which is large enough for
performing in situ analysis or processing of the substrate or the plasma.
To this end, the beam path is directed to the substrate and focused by
the lens at an angle of incidence to the substrate of zero degrees. The
area of the optical feedthrough is indicated by reference number 5. The
cone of the feedthrough 5 with the smaller opening directed at the
substrate advantageously allows more back-radiation from the substrate to
be gathered by the lens than in the case of a simple hole feedthrough as
in FIG. 3. The metallic shielding 4, represented by the dotted line, is
disposed on the side of the feedthrough 5 facing the substrate. The
shielding can be soldered into a groove in the optical feedthrough for
this purpose. Reference number 3 indicates a height-adjustable converging
lens in the support of the plasma chamber.

[0067] FIG. 2 shows a section of a showerhead electrode arrangement
according to the invention, with three gas distribution plates fitted
into a stainless steel support 39. In the section view, a first gas
distribution plate 32 can be seen facing the substrate (not shown in the
FIG., but theoretically disposed above the electrode 31). This first
plate is fastened to the support with two screws 37. A second gas
distribution plate 33 and a third gas distribution plate 34 are separated
from one another by spacer ring 38. The diameter of the gas distribution
plates continuously increases from gas distribution plate 32 to gas
distribution plate 34. The hole in plate 32 has an inside diameter of 10
mm, the hole in plate 33 is 16 mm and the hole in plate 34 is 19 mm in
diameter.

[0068] Reference number 35 indicates a stepped funnel as a physical
component. The funnel 35 has edge steps directed outward, on which the
gas distributor plates 32, 33 and 34 sit. A protruding border, which is
provided with two or more bores in the edge thereof, is disposed at the
lower end of the funnel. The bores are provided for screws 36. Only the
left of the two screws 36 is given a reference number. The entire
electrode 31 comprising the plates and the support 39 is fastened in the
plasma chamber using ceramic supports 52 as shown in FIG. 4.

[0069] The gas distribution plates 32 to 34 facilitate a homogeneous gas
distribution in the plasma space (at the top in the drawing). By
providing an increasing number of gas distribution holes per gas
distribution plate, from bottom to top in the drawing, the required
pressure gradient is achieved. This causes the gas to flow homogeneously
from the uppermost plate 32 into the plasma chamber thereabove. To this
end, the gas is first introduced to the areas located below plate 34. The
funnel in the optical feedthrough prevents the gas from exiting through
the optical feedthrough and keeps it gas-tight.

[0070] The angle of the cone and the size of the feedthrough 35 through
the hole pattern in the gas distribution plates is determined by the
three gas distribution plates themselves. These should be altered as
little as possible by the feedthrough 35. The diameter of the upper
opening of the feedthrough in the cone is 1 cm, and the diameter of the
lower opening is 2.2 cm.

[0071] The conical feedthrough was selected so to achieve as large
acceptance angle as possible for gathering electromagnetic radiation,
with a small opening in the upper electrode. In the present case, the
showerhead electrode has a diameter of 13.7 cm. Industrially, however,
substrate sizes of up to 5.7 m2 are now being coated. Furthermore,
the substrate does not have to be located above the electrode 32. The
showerhead electrode can also be above the substrate. This would
correspond to the arrangement in FIG. 2 "upside down." Furthermore, the
electrode and the counter-electrode can be arranged vertically. This
corresponds to tilting by 90°.

[0072] FIG. 3 schematically illustrates placement in a vacuum chamber 41
according to the invention. Due to the arrangement of the turbopump 47 in
this example, a straight-line radiation path is not possible, making the
45° turn using the mirror 46 necessary, The distance from the RF
electrode 44 according to the invention, and thus the distance of the
lens 45, to the substrate 43 is height-adjustable and variable from
approximately 5 mm to approximately 25 mm. This corresponds to the
distances used in industry for the deposition of silicon during the PECVD
process. Reference number 42 indicates the counter-electrode where the
substrate 43 is located. An excitation laser, not shown, generates the
radiation 48, which is focused onto the substrate or a layer deposited
thereon, through a window 50 in the chamber wall and through the
converging lens 45. Reference number 49 indicates the (Raman) radiation
gathered by the lens, the radiation being supplied through the lens 45 to
the mirror 46. The radiation 49 is directed by the mirror 46 to the
spectrometer (not shown) for further analysis. The angle of incidence is
zero degrees.

[0073]FIG. 4 shows the practical application of FIG. 3 in a technical
cross section. The plano-convex converging lens 56 focuses the excitation
radiation onto the sample and gathers the Raman radiation (not shown).
The focal length of the lens 56 is selected such that the substrate
surface lies at the focal point (here 38 mm). The lens 56 is held in
place in the support with a screw 55.

[0074] The small glass plate 60 above the lens 56 was installed to prevent
the lens from being coated during the deposition of the sample layer (not
shown). This allows the optics to be cleaned easily, which is
advantageous. The optical feedthrough is not shown in this figure. To
couple the radiation in and out, a mirror 61 is disposed at a 45°
angle relative to the support.

[0075] The mirror 61 is disposed in a support together with the lens 56.
This support 53 is attached to the electrode in a height-adjustable
manner so that different distances between the electrode and the layer
and the layer itself can be spectroscopically examined variably. The
height-adjustability is made possible by a screw in a slot (cannot be
seen in this drawing).

[0076] FIG. 5 shows the in situ measurement of the intensity of the Stokes
shift as a function of the magnitude of the shift, made possible by the
RF electrode construction according to the invention with the optical
feedthrough and placement in the plasma chamber--this measurement is the
basis of Raman spectroscopy. Shown are measurements at different stages
of layer deposition. After approximately 12 nm of deposited silicon
layer, a signal can be seen which can be associated with the glass
substrate. After approximately 240 nm, the measurement signal shows a
typical characteristic for microcrystalline silicon. The Stokes shift of
microcrystalline silicon can be broken down into two portions. The first
portion is caused by the microcrystalline phase and has an intensity
maximum at -520 cm-1. The second portion is caused by the amorphous
phase. Its intensity maximum is at -480 cm-1. Since the deposition
takes place at approximately 200° C., the intensity maximum of the
microcrystalline phase is at a Stokes shift of approximately 505 relative
wavenumbers, and the intensity maximum of the amorphous phase is
˜460 cm-1. At a deposited layer thickness of approximately 720
nm, the signal is even more pronounced since the contribution from the
glass substrate has now been completely suppressed.

[0077] FIG. 6a) shows the in situ measurement of the intensity of the
optical emission of the plasma as a function of wavelength in a range of
505 nm to 570 nm, made possible by the electrode construction according
to the invention with the optical feedthrough and placement in the plasma
chamber. If the measurement is done in a larger spectral range, as shown
in FIG. 6b), the ratio of two emission lines, for example, can be used to
determine gas concentrations in the plasma.

Patent applications by Aad Gordijn, Juelich DE

Patent applications by Reinhard Carius, Juelich DE

Patent applications in class With Raman type light scattering

Patent applications in all subclasses With Raman type light scattering